Such a contactor, in general terms, includes a movable core of a solenoid, this core being connected at one end to a pivoting lever, its other end being connected to the driving element of the meshing device of the starter. During its displacement, the movable core displaces a movable electrical contact which is arranged to cooperate with fixed contacts, so as to make the electrical supply to the starter motor.
Despite all the precautions that may be taken during the manufacture of such a contactor, so as to ensure sealing which is as perfect as possible, it has been found that particles of dirt, which is generally of electrically insulating material, can still penetrate into the interior of the housing of the contactor, and may in particular become deposited on the fixed contacts of the latter, thus giving rise to electrical discontinuity and therefore failure of the starter system as a whole to function at all.
Experience shows that this situation is particularly frequent when the movable contact is flat and is arranged to engage with fixed contacts of the kind having terminal elements of generally spherical shape. In this connection, in such a context the mechanical, and therefore electrical, connection is obtained for each fixed contact at a single point, which is always the same point throughout operation of the contactor. It therefore only needs a few insulating particles to cause the malfunction described above to occur, with its consequent interruption of the electrical supply.